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-* Control statements
-*** Outline
-***** Introduction
-******* What are we going to do?
-******* How are we going to do?
-******* Arsenal Required
-********* working knowledge of arrays
-
-*** Script
- Welcome.
-
- In this tutorial we shall be covering conditional statements and
- control loops. We have used them already in some of our previous
- sessions with brief introduction. We shall be covering 'if-else'
- statement, 'while' and 'for' statements formally.
-
-
- For understanding of if-else statement we will write a python
- script that takes a number as input from user and prints 0 if it is zero
- and prints "Be positive" if it is negative, prints "Single" if the input is 1
- and if the number is not 0 or 1 or negative, it prints "More".
-
- To write the program, open Scite text editor by going to Applications->
- Programming->Scite:
-
- First we prompt user for entering a integer by using raw_input
- str_x = raw_input("Enter an integer: ")
- since we know raw_input gives string, we convert the input string to an integer
- by typing
- x = int(str_x)
-
- now we check if the number is less than zero.
- type
- if x < 0:
- Please not
- #if number is negative we have to print "Be positive"
- #so we give four spaces for indentation and type
- print 'Be positive!'
-
- elif x == 0:
- to check if the number is equal to zero
- #This is else-if condition
- print 'Zero'
- elif x == 1:
- print 'Single'
- then we type the else statement which gets executed when all the if and elif statements fail
- so type
- else:
- print 'More'
-
- Save this script by going to file menu and clicking on save.
- save it in home folder with name 'ladder.py'
-
- let us check the program on ipython interpreter for various inputs
- open ipython terminal and type
- %run ladder.py
- It will prompt us to enter a integer and based on our input it
- prints appropriate message.
-
- We can use binary operators like and/or/not to check for multiple
- conditions.
-
- Python supports only if-elif-else conditional constructs,
- switch-case statements are not available/supported in Python.
-
- Now lets look at loop constructs available. Python supports 'while'
- and 'for' statements.
-
- To understand the while we shall write a script that prints all the fibonacci
- numbers less than 10. In fibonacci series the sum of previous two elements
- is equal to the next element.
-
- In Scite go to file menu and click on new and it opens a new tab.
-
- First we initialize two variable to first and second number of
- series
- a, b = 0, 1
- while b < 10:
- This block will be executed till this condition holds True
- print b,
- Note ',' here for printing values in one continues line.
- a, b = b, a+b
- This is one powerful feature of Python, swapping and assigning
- new values at the same time. After this statement a will have
- present 'b' value and b will have value of 'a+b'(phew this can be close)
-
- Save this file as 'fabonacci.py' and lets run it from IPython
- interpreter by
- %run fabonacci.py
-
- 'for' in python works any kind of iterable objects. In our
- previous sessions we used 'for' to iterate through files and lists.
-
- So we are going to use for loop print the squares of first five whole numbers.
-
- To generate squares, we have to iterate on list of numbers and we are
- going to use the range function to get the list of numbers.
-
- let us look at the documentation of range function by typing
- range?
- we see that it takes three arguments, first is the start/initial value
- second one is the stop/last value and third is the step size.
-
- Out of these, 'start' and 'step' arguments are optional.
-
- So to get list of first five natural numbers, we use
- range(5)
-
- Note here that last/stop value is not included in resulting list.
-
- So to get square of first five number all we have to do is
- iterate over this list.
- for i in range(5):
- ....print i, i*i
- ....
- ....
-
- Similarly to get square of all odd numbers from 3 to 9 we can do
- something like
-
- for i in range(3, 10, 2):
- so the list returned from range this time will start from 3 and
- end at 10(excluding it) with step size of 2 so we get odd numbers
- only
- ....print i, i*i
- ....
- ....
-
- since the for statement in python works on any iterable we can also iterate through strings
-
- to print each character in a string we do
- for c in "Guido Van Rossum":
- print c
-
- we see that it prints all the characters one by one
-
- That brings us to the end of this tutorial. We have learnt
- conditional statements in Python. How to write loops
- using 'while' statement. Range function and using for loop
-
-
- Thank you!
-
-*** Notes
-